In its broadest sense, the term "dextrin" covers any starch degradation products, with the exceptions of mono- and oligosaccharides, regardless of how the starches are degraded. All dextrins belong to a large and varied group of D-glucose polymers which can be linear, highly branched, or cyclic. Their complexity creates problems in any classification based on their chemical character. Hence, they are often classified based on how they are prepared.
The hydrolytic procedures used for their preparation fall into four major groups: products obtained by hydrolysis of dispersed starch by the action of liquefying enzymes such as amylases; products obtained by the acid hydrolysis of dispersed starch; Schardinger dextrins formed from dispersed starch by the action of Bacillus macerans transglycosylase; and pyrodextrins produced by the action of heat or heat and acid on dry starch.
Maltodextrins include enzyme- and/or acid-converted dextrins, defined by the Food and Drug Administration (FDA) as non-sweet, nutritive saccharide polymers which consist of D-glucose units linked primarily by alpha-1.fwdarw.4 glucosidic bonds and which have a dextrose equivalent (DE) of less than 20. Corn syrup solids are defined by the FDA as dried glucose syrups in which the reducing sugar content is 20 DE or higher. The degree of hydrolysis strongly affects the functional properties of maltodextrins and corn syrup solids.
Manufacturing processes for preparing maltodextrins include single-stage and dual-stage starch slurry processes using acid and/or enzyme. A solids content of about 18-35% is considered high solids.
A single-stage process combines either acid or enzyme conversion at relatively high temperatures with gelatinization of the starch. The hydrolysis may then be continued in hold tanks until the appropriate DE is reached, at which point the hydrolysis is terminated by either pH adjustment or heat deactivation. The product may then be refined or purified, concentrated and spray-dried.
A dual-stage process involves first a high temperature (usually &gt;105.degree. C.) gelatinization/liquefaction with either acid or enzyme to a low DE (usually &lt;3) followed by a high temperature treatment (as in a jet cooker) to ensure gelatinization of the starch. After pH adjustment and lowering of the temperature to around 82.degree.-105.degree. C., a second conversion step, usually with a bacterial alpha-amylase, is conducted until the desired DE is achieved. The enzyme is then deactivated and the product may then be refined and spray-dried.
Some of the patents covering acid- and/or enzyme-conversion of starches to maltodextrins are discussed below.
U.S. Pat. No. 2,609,326 (issued Sep. 2, 1952 to W. W. Pigman et al.) discloses rapidly gelatinizing and dispersing starch granules in hot water while subjecting the starch to intense agitation and shearing, immediately converting the gelatinized and dispersed starch at an elevated temperature with a starch-liquefying amylase characterized by its ability to hydrolyze the starch molecules into large fragments, inactivating the enzyme, and immediately drying the enzyme converted starch. The dry cold water dispersible converted starches are characterized by a very low content of reducing sugars (3% or less).
U.S. Pat. No. 3,560,343 (issued Feb. 2, 1971 to F. C. Armbruster et al.) discloses a process where a starch is acid hydrolyzed to a D.E. less than 15 and then converted with a bacterial alpha-amylase to a DE between 10 and 25.
Japanese 46-14706 (published Apr. 20, 1971) discloses a continuous process for preparing a granular converted starch which swells, but does not dissolve in cold water, and which is reduced in viscosity. A starch alpha amylase mixture having a water content of 40-60%, containing buffer to adjust the pH to 5-7, is cured for several hours at room temperature, or a temperature at or below the gelatinization temperature, after which it is put into a starch dryer maintained at 70.degree.-150.degree. C. During the drying, the temperature and water content change to those suitable for hydrolyzing the starch. The hydrolysis, drying of the hydrolyzed starch, and deactivation of the residual enzyme simultaneously occur during the heating at 70.degree.-150.degree. C. A liquefaction-type amylase shows the strongest hydrolytic activity at 70.degree.-90.degree. C., but at higher temperatures (i.e., above 90.degree. C.), if the moisture content is above 35%, the starch undergoes the hydrolytic activity but is gelatinized at the same time and if the water content of the mixture is less than 30%, it becomes more difficult to gelatinize the starch, but at the same time the hydrolysis by the enzyme shows a tendency to fall off rapidly. To satisfy these opposing tendencies, it is necessary to reduce the water content of the mixture from 40-60% to 30-35% in the dryer and to increase the temperature to 90.degree.-100.degree. C. during the enzyme hydrolysis.
U.S. Pat. No. 3,849,194 (issued Nov. 19, 1974 to F. C. Armbruster) discloses treating a waxy starch with a bacterial alpha-amylase at a temperature above 85.degree. C. to liquify the waxy starch, cooling the liquified waxy starch to about 80.degree. C., and converting the liquified waxy starch with the bacterial alpha-amylase to a D.E. of from about 5 to about 25.
U.S. Pat. No. 3,663,369 (issued May 16, 1972 to A. L. Morehouse et al.) discloses a two-stage hydrolysis. The first stage is carried out with acids or enzymes at elevated temperatures for short periods to liquify the starch with very little dextrinization or saccharification. The second stage is carried out at an alkaline pH with bacterial alpha-amylase to achieve the desired D.E.
U.S. Pat. No. 3,853,706 (issued Dec. 10, 1974 to F. C. Armbruster) discloses hydrolyzing starch with a bacterial alpha-amylase to a D.E. of less than 15, terminating the hydrolysis by heat treatment, and further converting to a DE of between about 5 and 20.
U.S. Pat. No. 3,974,034 (issued Aug. 10, 1976 to H. E. Horn) discloses maltodextrins which are prepared by the enzymatic hydrolysis of an oxidized starch. The starch is first simultaneously liquefied and oxidized at elevated temperatures and then converted with a bacterial alpha amylase to a D.E. not substantially above 20.
U.S. Pat. No. 4,014,743 (issued Mar. 29, 1977 to W. C. Black) discloses a method for the continuous enzyme liquefication of starch. Preferably, the starch is a raw starch, but pregelatinized or modified starches may be used (see Column 6, lines 1-7). A suitable enzyme is bacterial alpha amylase. An enzyme-containing suspension of raw starch (10-45 wt. % on a dry solids basis) is continuously added to an agitated body of heated (77.degree.-99.degree. C.-170.degree.-210.degree. F.) converted starch. The incoming starch is gelatinized and mixed with the partially converted starch to maintain a blend having a viscosity low enough to be readily agitated and pumped. A stream of the blend is continuously removed from the conversion tank and treated to inactivate the enzyme. The process is controlled to limit the maximum viscosity of the blend to a Brookfield viscosity of not over 5000 cps (100 rpm and 88.degree. C.-190.degree. F.). The reducing sugar content is usually less than 3% on a dextrose equivalent basis. A blend of starches that have been subjected to different degrees of enzyme conversion is obtained since the heating and enzyme treatment is not uniform for the individual starch granules or molecules.
U.K. 1,406,508 (published Sep. 17, 1975) discloses a continuous process for liquefying natural or chemically modified starch to give starch pastes having a solid content of up to 70% by weight. The starch in granular form, without the intermediate formation of a slurry, is continuously supplied to a reaction zone where it is subjected to the action of an enzyme (e.g., alpha amylase) in a stirred aqueous medium at an elevated temperature (50.degree.-98.degree. C.) and pH of 4.5-8. Once the liquefaction is completed the liquefied starch is stabilized by deactivating the enzyme. A greater proportion of large molecules and a broader molecular weight distribution results as compared to a discontinuous process where the molecules are smaller and substantially the same size.
DE 37 31 293 A1 (laid open Apr. 8, 1980) discloses a process for continuously degrading and digesting starch. A dry starch powder together with liquid water or an aqueous starch suspension is charged to a stirred converter containing a starch degrading enzyme, preferably alpha amylase, while the temperature is increased to 70.degree.-90.degree. C. by the injection of steam at 120.degree.-125.degree. C. and 2-4 bar. The product leaving the converter is treated with an enzyme deactivating agent before final dilution to the desired concentration.
U.S. Pat. No. 4,921,795 (issued May 1, 1990) to F. A. Bozich, Jr.) discloses an improved slurry method for producing dextrin adhesives using alpha amylase in combination with glucoamylase. The function of the glucoamylase is to eliminate the limit dextrin problem and the mechanical shearing step. The alpha amylase randomly cleaves the .alpha.(1.fwdarw.4) linkages of the linear amylose molecules and cleaves the branched amylopectin molecules up to the (1.fwdarw.6) glucosidic linkages of the limit dextrin. The slurry is stirred sufficiently to create a vortex in the aqueous reaction slurry, thereby maintaining adequate mixing without shearing. The hydrolysis is allowed to continue until an optimal mix of fragment sizes is achieved (as indicated by a Brookfield viscosity of 1000-2000 cps at 20 rpm, 110.degree. F., 45-55% solids, and 0 to 16% sodium borate pentahydrate). The enzyme is then inactivated. The Theological properties of the resultant slurry can be adjusted as needed.
There is a need for high solids, stabilized (i.e., chemically derivatized) maltodextrins which can be used where pyrodextrins or maltodextrins are conventionally used, for example in remoistenable adhesives.